DESIGN OF COCKPIT GRAPHICS (EXAMPLE)

This page presents a brief example of how the design process described on the color graphics design page might be applied to a cockpit display.

Information display in aerospace cockpits is demanding due to the high stakes and rapid decisions in the initial and final phases of flight. The aircrew need to maintain awareness of numerous factors. Individual data displays are typically only one part of a cyclical scan of multiple displays and the out-the-window scene. Demands to manipulate displays must be kept to an absolute minimum (preferably none). The ambient light environment varies from high daytime illuminations to nighttime levels. These constraints call for extremely clear, very high-information-density displays.

Prototype Color Design for an Integrated Display of Hazard Information

At the outset we have to emphasize that this example represents just an initial draft of the display and associated user operations. In good design practice every decision regarding the data set to be displayed, the associated user procedures, and the data hierarchy should be initially reviewed by the design team (human factors experts, subject matter experts, and engineering experts) and then re-examined several times during the course of an iterative development process of design/test/redesign/retest.

Starting Point. The starting point for the integrated hazard display was NASA's AMES display, a prototype display of integrated navigation and traffic information intended to be viewed on the navigation display of commercial airliners. The AMES design represents a substantial development effort over several years. It is consistent in content and graphics with existing display of navigation data and TCAS traffic data. It integrates further traffic data obtained either from automated position reports from other aircraft or from ground surveillance. It also includes the graphics of software tools that help the pilots plan conflict-free routes.

The color scheme of the AMES display includes labeling of altitude relations, manipulation of luminance contrast for attention management, and honoring of most cultural and prior cockpit color-coding conventions and standards. Symbols for aircraft above, at, or below ownship altitude are blue, gray, and tan, respectively. Context graphics (e.g., static labels and framework graphics) and symbols for aircraft at distant altitudes are coded in lower luminance contrasts than more urgent data.

This example design extends the AMES display to include other hazards. The existing air traffic and navigation functionality and data are adopted without modification, but the color design for the pre-existing elements is revisited as part of the new overall color design.

Phase 1: Data Planning

Data Inventory / Data Analysis . The data to be displayed are the traffic and navigation data of the AMES display, plus:

3D Terrain Data, with Hazard Detection--These are assumed to be based on a terrain database similar to those underlying the current Enhanced Ground Proximity Warning System. The system's logic is assumed to automatically identify terrain that poses no hazard, terrain that warrants a caution, and terrain that warrants a warning, based on the aircraft's state and capabilities.

Weather Data, with Tops and Vectors--For this example the weather data are assumed to be NEXRAD radar plus maximum altitudes and motion vectors of the weather.

Some further data details are derived from consideration of operational constraints. The altitude resolution required for the display of the currently-non-hazardous terrain needs careful analysis in terms of the pilots' tactical and strategic needs. From usage in aviation charts we assume, for this example, that a coarse (five or six levels) contour map is sufficient to support navigational orientation and early awareness for trajectory changes. A representation with more levels, should it prove justified, would place even more demanding constraints on the color design.

Attention Management. The data were sorted into categories and the categories ordered in a hierarchy of urgency. This urgency hierarchy provides the rationale for designing saliences of the various graphic elements of the display.

The most urgent category includes the immediately hazardous terrain, weather, and traffic. Within this category there is a secondary ordering, with terrain threats being more certain than weather and traffic, but all three deserve the highest possible salience.

The next category is data involved in the immediate flying of the plane. They include the symbol for this aircraft, its immediate trajectory, and current state variables (heading, altitude, and speed). The main location for display of most of these data is the primary flight display, but they are echoed on this navigation display to avoid the need to look back and forth while planning trajectories.

The next lower category includes aircraft on 3D trajectories that potentially pose a future traffic hazard for ownship.

The next lower category is data reporting the active states (if any) of the software course-planning tools.

The next lower category includes dynamic elements that require monitoring but aren't currently involved in immediate decisions. These include aircraft at altitudes sufficiently different from ownship's that they pose no traffic hazard, non-hazard terrain, and non-hazard weather.

Next is context alphanumerics and lines that delineate features that might be the focus for some user action. This includes labels on virtual pushbuttons and compass markings to be read.

The lowest urgency category is static elements that provide spatial structure to the display. The fixed labels on the speed and altitude readout locations and outlines of virtual pushbuttons are examples.

Phase 2: Design of the Graphics Implementation

The hierarchy of data urgency provides the guidance for the design of the graphics, including color assignments.

Design perceptual layers using achromatic color. The first issue was choice of contrast polarity. Traditional cockpit displays were "radar-like", with bright symbols on dark backgrounds. As display, computing, and communication technologies have matured, more and more commercial displays for the cockpit are incorporating area variables, e.g., moving maps with terrain and weather. Future cockpit displays are likely to migrate to a "map-like" design, with dark symbols on light backgrounds. We chose this second polarity for this example.

The next step was to design achromatic graphics that gave the graphic elements salience that corresponds to the urgency hierarchy. In this prototype only luminance contrast was manipulated for attention control, but font size and stroke width could provide further distinctions.

In this color design, symbols and alphanumeric data involved in the immediate flying of the plane were assigned high luminance contrast, to give them the highest salience during routine flight conditions. Aircraft that might pose a future traffic hazard were also given high luminance contrast. Aircraft unlikely to pose a future traffic hazard were given noticeably lower luminance contrast. Context data--lines, symbols, labels, and non-hazard area variables--were coded at low luminance contrasts to give them the least salience without actually removing them.

That leaves only the urgent data. These data were made to stand out by use of chromatic color. While not included in this prototype, various degrees of temporal modulation (blinking and flashing) and possibly auditory signals might also be used to further increase the salience of the most extreme, unusual hazards, should they prove necessary.

Decide where chromatic color will be used and why. Chromatic color is used sparingly in this prototype, for specific purposes. The most important usage is caution-and-warning color codings for symbols of aircraft predicted to be a traffic hazard, for hazardous terrain, and for weather. The colors give these high urgency data specific, culturally conventional labels and provide still higher salience through "popout". Chromatic color is also used to visually group classes of aircraft. Static grouping includes groups of aircraft above, below, and at the ownship altitude. Data relating to planning waypoints are visually grouped by means of chromatic color. Status of pushbuttons for route-planning tools was indicated by chromatic infills. Representation of altitudes of non-hazardous terrain was accomplished with grayscale shading and did not require chromatic color.

Choose colors. The color choices were based on a number of considerations. Cultural constraints and standards were considered first in selecting hues and saturations for labeling the hazard data. Warning status and caution status required saturated red and saturated yellow or yellow-orange, respectively. Terrain hazards were labeled with striped texture, to make a distinction from weather hazards and to provide high salience.

The luminance values were chosen on the basis of perceptual layering demands. Very pale green was used for low intensity weather for several reasons. The areas covered by low intensity weather can be quite large, and aircraft often fly through it. Use of a low-saturation green for this level of weather allows high luminance-contrasts with aircraft and other symbols. It also avoids simultaneous- and successive-contrast problems that can occur with large areas of saturated color. Warning-level weather is usually confined to small areas so the relatively low luminance of high-saturation red is a minor problem. Caution-level weather also tends to be small, and maximum purity and high luminance can be gotten simultaneously in yellow. Five levels of gray were used to label the altitudes of terrain, with the darkest still light enough to allow high luminance-contrast for aircraft symbols and alphanumerics.

Discriminability and identifiability then came into play as the hazard labeling reduced the options for other coding colors. Aircraft above and below ownship were labeled in blue and brown, respectively, dark enough to preserve the high luminance-contrast required by their position in the urgency hierarchy, but not so dark as to make identification problems. Aircraft at the same altitude as ownship were coded gray. Magenta is conventionally used for ownship flightpath, and was also used as the grouping color for the trajectory planning data elements.

Current cultural usage and aviation standards require that aircraft in warning status (due to traffic conflict or declared emergency), hazardous terrain and hazardous weather all be coded in saturated red. The big problem was distinguishing the two classes of area variables. The proposed solution is for the terrain hazard to be labeled with alternating stripes of black and hazard color. This makes a distinctive, salient pattern for this high-probability hazard. The masking effects of the texture on other line graphics is probably an acceptable price for this payoff, but this needs careful testing. It seems unlikely that a red aircraft would often be in the middle of red weather. When this occurs, the proposed solution is outlining the aircraft symbol in white.

More generally, the presence of numerous patches of high-salience red and yellow weather cells may interfere with attention to important aircraft data. This would require that some of the salience be toned down by using less saturated red and yellow.

As the interface undergoes successive stages of testing these problems and unanticipated problems may require redesign of part or all of the color scheme. These redesigns must be done with as much or more care than the initial design, and the required time and money should be identified at the beginning of design.

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